Unusual Enhancement in Tear Properties of
Single-Site LLDPE Blown Films at Higher Draw-Down Ratio
Nitin Borse, Norman Aubee, Paul Tas
NOVA Chemicals Technical Centre
ABSTRACT
Anisotropy is generally observed in the machine direction (MD) and transverse direction (TD) tear strength
properties of polyethylene blown films prepared at high draw-down ratios. This study investigates the tear strength
of blown films prepared from different linear low density polyethylenes (LLDPE) at different draw-down ratios.
Conventional Zeigler-Natta catalyzed (Z-N LLDPE) and single-site catalyzed (sLLDPE) resins were used. The films
were analyzed using Raman spectroscopy, optical microscopy and wide-angle X-ray scattering (WAXS) for pole
figures analysis. We observed that the TD tear strength correlated with crystalline phase orientation in the films, and
MD tear strength correlated with orientation in both the crystalline and the amorphous phases. The Z-N LLDPE
blown films showed higher MD orientation of crystalline and amorphous phases at higher draw-down ratio. The
sLLDPE blown films showed higher crystalline MD orientation at higher draw-down but the overall orientation was
higher in TD. This anomalous orientation behavior in sLLDPE blown films resulted in unusually high TD and MD
tear properties at higher draw down.
INTRODUCTION
Linear Low Density Polyethylene (LLDPE) resins are mostly used in film applications. Although different film
market segments have different performance requirements, superior tear, tensile and dart impact strength are always
desirable. Packaging films are required to possess high tear resistance in most applications. The tear resistance of the
films, along with the other physical properties, depends upon the molecular architecture, microstructure and
molecular orientation. It has been recognized [1] that film performance strongly depends upon the orientation of
both the crystalline phase and the amorphous chains.
There have been attempts to correlate the properties of polyethylene blown films to morphology and orientation.
Krishnaswamy and Sukhadia [2] found that the MD tear strength of LLDPE blown films was higher when noncrystalline chains were close to equi-biaxial in the plane of the film, while the TD tear strength was higher when the
crystalline lamellae were relatively straight and close to the TD. Krishnaswamy and Lamborn [3] explained the
differences in the tensile properties of LLDPE blown films between the MD and TD in terms of lamellar orientation.
There are attempts to relate the orientation, morphology and properties of the blown polyethylene films to the
MD/TD stress balance at the frost line [4, 5] and draw down ratio [6]. Chen et al. [1] fabricated LLDPE films at
different conditions of blow up ratio, die gap, and frost line height. The films were analyzed for White-Spruiell
orientation factors of crystal unit cells, amorphous chains and Herman’s orientation factors of lamellae from wideangle X-ray scattering (WAXS) pole figures, birefringence and small angle X-ray scattering (SAXS). They found
that in typical Z-N LLDPE films the amorphous chains were aligned preferentially along the MD. The results show
that at higher draw down the TD tear strength was higher, but MD tear strength and dart impact strength were
reduced. Zang et al. [7] studied oriented structure and anisotropy properties of polyethylene blown films. The Z-N
LLDPE films with octene comonomer showed higher tear strength than those produced using butene comonomer.
The butene comonomer Z-N LLDPE films showed higher anisotropy in MD/TD tear strength. However in both the
films the MD tear strength was reduced at high draw-down ratio.
In this study we prepared sLLDPE, Z-N LLDPE, mLLDPE and super-hexene LLDPE films at low and high drawdown conditions by varying blow up ratio, film processing speed and film gauge. The films were tested for MD and
TD tear strength. The crystalline and amorphous phase orientations were analyzed for White-Spruiell orientation
factors of crystal unit cells by wide-angle X-ray diffraction (WXRD). The film crystallinity was analyzed by Raman
spectroscopy. Polarized optical microscopy technique was used to estimate MD/TD birefringence of the films. The
unique tear behavior was observed in sLLDPE films, where both the MD and the TD tear strength were significantly
higher at high draw ratio. The tear properties of LLDPE films are explained in terms of the orientation of molecular
chains in crystalline and amorphous phases in the films.
BACKGROUND
Development of fundamental structure–property–processing conditions relationships in polyethylene films is of
great importance in understanding blown-film characteristics. Understanding morphology and different structures in
blown films is the first step towards this development. A hierarchy of structure exists in commercial polymers. A
well defined crystalline structure generally exists at dimensions on order of magnitude in Angstrom units [8]. A
lamellar structure is found at dimensions of order 20-200 Å. Spherulites exist with dimensions of about 1 μm.
Important parameters to determine in processed films are the level of crystallinity and the level of polymer chain
orientation. The method first described by Herman and Platzek [9] to measure orientation in fibres was
determination of birefringence by optical retardation in a polarized light microscopy. The birefringence is defined as
the difference in the refractive indices between two perpendicular directions. In semi-crystalline polymers, both
crystalline and amorphous phases possess different orientation levels. The measured birefringence is the sum of the
contributions from both these phases.
The crystalline structure of polyethylene was first determined by Bunn [10] in 1939 using a long chain branched
polyethylene (LDPE) on the basis of wide-angle X-ray diffraction studies. Polyethylene is found to crystallize into
an orthorhombic unit cell with dimensions of a, b and c-axes as 7.41, 4.94 and 2.54 Å respectively. The crystal
growth is seen in the direction of b-axis, and c-axis is the polymer chain axis. The crystalline phase orientation is
usually analyzed by wide-angle x-ray scattering (WAXS) and then constructing pole figures [1]. This allows a
complete representation of the distribution of polymer chains and crystallographic axes. In blown films it is seen that
a-axis shows orientation towards MD whereas b-axis orients itself in TD.
White and Spruiell [11] developed the representation of a series of second moment biaxial orientation functions,
which are useful for characterizing molecular orientation in films and sheets. Figure 1 shows the White-Spruiell
triangular representation of orientation of crystalline axes in a film. By knowing the relative orientation of all three
axes (namely a-, b- and c-axis) of a unit crystal, the overall crystalline orientation in the film could be visualized.
A
1
D
TD →
0.5
E
G
B
0
-1
-0.5
0
0.5
1
-0.5
F
-1
C
MD →
Figure 1: White-Spruiell representation of crystalline axis orientation in the films
A: TD only; B: MD only; C: ND only; D: MD/TD equi-biaxial;
E: TD/ND equi-biaxial; F: MD/ND equi-biaxial; G: isotropic
The amount of amorphous orientation in the blown films can be estimated by assuming the simple two phase model
for polyethylene [1, 12]. In this case, the total birefringence can be represented by,
Δ MN = nM − nN = w[Δocbc f cc,MD + Δocab f ac,MD ] + (1 − w)Δoa f am ,MD
(Equation 1)
Δ TN = nT − nN = w[Δocbc f cc,TD + Δocab f ac,TD ] + (1 − w) Δoa f am ,TD
(Equation 2)
where
w : film crystallinity (by Raman spectroscopy)
nM , nN , nT : refractive indices in Machine, Normal and Transverse direction of film
fcc, fac :crystalline orientation functions of c and a-axis of PE unit crystal (by GADDS pole figure analysis)
Δ MN , Δ TN are MD/ND and TD/ND Birefringence
fam,MD and fam,TD are MD and TD amorphous orientation function
Δocbc , Δocab are intrinsic birefringence values of PE crystals in respective direction
Δocbc = 0.056, Δocab = −0.005
Δoa intrinsic birefringence of amorphous phase = 0.058
Subtracting equation 2 from equation 1, leads to the equation in terms of MD/TD birefringence, which contains the
term showing the difference in the amorphous orientation between MD and TD.
Δ MT = w[Δocbc ( f cc,MD − f cc,TD ) + Δocab ( f ac,MD − f ac,TD )] + (1 − w)Δoa ( f am,MD − f am,TD )
(Equation 3)
where Δ MT = Δ MN − Δ TN = nM − nT = MD/TD Birefringence (by optical microscopy)
Using equation 3 the difference in MD and TD amorphous phase orientation functions (fam,MD – fam,TD) can be
calculated by knowing the overall orientation obtained from the MD/TD birefringence analysis.
We obtained pole figure analysis and the MD/TD birefringence for all the LLDPE films produced under low and
high draw-down conditions. The tear properties of the films were correlated with crystalline orientation functions,
MD/TD difference in amorphous chain orientation functions and the overall polymer chain orientations.
EXPERIMENTAL
Materials
Three sLLDPE, two Z-N LLDPE, one m-LLDPE (metallocene catalyzed LLDPE) and one super-hexene co-polymer
LLDPE resins were blown into films at low and high draw-down conditions. The following Table gives the material
characteristics.
Table 1: Material characteristics
Product
Reference Name
in This Paper
Co-monomer
Melt Index
(gm/10min)
Density
(g/cm3)
SURPASS FPs016-C
sLLDPE1
Octene
0.65
0.9160
SURPASS FPr018-D
sLLDPE2
Octene
0.86
0.9180
SURPASS FPs117-C
sLLDPE3
Octene
0.92
0.9170
SCLAIR FP020-C
Z-N LLDPE1
Octene
0.67
0.9210
SCLAIR FP120-C
Z-N LLDPE2
Octene
0.93
0.9200
COMP mLLDPE
mLLDPE
Hexene
1.18
0.918
NOVAPOL TD-9022-D
Sup hex LLDPE
Hexene
0.64
0.9195
Experimental Procedure
All films were produced on a Macro 8” blown film line, equipped with a general purpose 3.5” single screw with
barrier design and length to diameter ratio 30. A general-purpose spiral die was used; the die diameter was 8” and
the die gap 50 mil. The cooling unit consisted of a dual lip air ring in combination with internal bubble cooling
(IBC).
Table 2: Blown film processing conditions
Film gauge
(mil)
Blow-Up
Ratio
Line Speed
(ft/min)
Draw-Down
Ratio
Low DDR
1.5
3:1
130
10.4
High DDR
0.75
2:1
390
30.5
All the films produced were tested for the Elmendorf tear strength as per ASTM D1922 in machine direction (MD)
and transverse direction (TD).
The film crystallinity was determined by Raman spectrometry using Renishaw inVia Raman spectrometer with air
cooled Argon ion 514.5 nm Laser.
Birefringence analysis of all the films was done as per ASTM D4093-95 using Olympus BX51 microscope with UCBR1 compensator for measuring the birefringence.
Crystalline orientation in the films was analyzed using the pole figure from the wide angle X-ray diffraction. The
pole figure method utilizes the General Area Detector Diffraction System (GADDS) manufactured by Bruker AXS
Inc. operating in the wide angle X-ray diffraction mode. The X-ray source was generated using a copper anode
which emits characteristic wavelength lines of Kα at 1.54 nm with nickel filter. The X-ray generator was set at 40
kV and 40 mA. The sample to detector distance was fixed at 4.90 cm. The films were rotated 180° at 5° intervals.
The diffraction pattern is then integrated for the (200) and (020) reflections. The results for the Hermans and WhiteSpruiell orientation functions obtained with the GADDS are represented in the form of White-Spruiell triangle plots
as shown in Figure 1.
RESULTS AND DISCUSSIONS
Film Crystallinity, Birefringence and Tear strength
Table 3 shows the results of crystallinity, birefringence and tear strength analysis of the films produced. Raman
spectrometry gives the three-phase analysis which includes interphase as an intermediate phase between the
crystalline and amorphous phases. In the present study, half of the interphase was taken as the part of the crystalline
phase and the other half as part of the amorphous phase. The positive sign of the birefringence indicates that the
overall orientation of the polymer chains in the film is in MD, and the negative sign indicates that it is in TD.
Table 3: Results of film analysis
Resin Type
sLLDPE 1
sLLDPE 2
sLLDPE 3
Z-N LLDPE 1
Z-N LLDPE 2
DDR
Raman film
Crystallinity
(%)
Birefringence
(MD – TD)
(X 10-4)
MD Tear
Strength
(gm/mil)
TD Tear
Strength
(gm/mil)
Low
37.8
– 4.63
272
445
High
36.7
– 7.83
783
658
Low
39.2
– 1.3
313
455
High
37.7
– 5.6
481
691
Low
38.7
0
313
502
High
36.6
– 3.83
595
753
Low
42.0
– 11.7
288
636
High
40.2
+ 16.33
116
917
Low
41.3
– 6.47
327
593
High
39.4
– 1.65
313
982
Low
40.4
+ 5.63
311
383
High
39.4
– 0.61
307
492
Low
38.8
– 7.31
456
592
High
36.3
– 13.13
350
888
mLLDPE
Sup hex LLDPE
Crystalline Orientation
Small and large data points are shown in Figures 2 and 3 to denote the two films prepared from each resin. The
small data point represents the film produced at low draw-down ratio (10.4) and the large data point represents the
film produced at high draw-down (30.5). The difference between the MD and TD orientation function is taken as the
measure of orientation, the positive values indicate MD orientation and then negative values indicate TD orientation.
The higher draw-down increases a-axis orientation in the MD and b-axis simultaneously shows higher orientation in
the TD. For all the films a- axis always showed orientation in MD and b-axis in TD. This means the crystal growth
direction in the films is always TD. As seen in Figure 3, the polymer chain axis (c-axis) shows MD orientation in
most films. As the draw-down ratio increases, c-axis MD orientation decreases. In the case of Z-N LLDPE2, the caxis orientation is in the TD at higher draw-down ratio. In the discussion that follows with respect to the crystalline
orientation, we consider the orientation of a-axis as the measure of the crystalline orientation in the films.
faMD‐faTD
0
0.05
0.1
0.15
0.2
0
sLLDPE1
sLLDPE2
fbMD‐fbTD
‐0.05
sLLDPE3
Z‐N LLDPE1
‐0.1
Z‐N LLDPE2
mLLDPE
‐0.15
Sup Hex LLDPE
‐0.2
Figure 2: Orientations of a- and b- axes of unit crystal in the LLDPE blown films
Small data point: low DDR (10.4); Large data point: high DDR (30.5)
0.08
0.06
sLLDPE1
0.04
fcMD‐fcTD
sLLDPE2
0.02
sLLDPE3
0
‐0.02
Z‐N LLDPE1
0
‐0.04
0.05
0.1
faMD‐faTD
0.15
0.2
Z‐N LLDPE2
mLLDPE
Sup Hex LLDPE
‐0.06
‐0.08
Figure 3: Orientation of a- and c-axis of unit crystal in LLDPE films
Small data point: low DDR (10.4); Large data point: high DDR (30.5)
Film Tear Properties and Polymer Chain Orientations
Machine Direction Tear Strength:
Figure 4 shows the plot of MD tear strength of LLDPE films and crystalline a-axis orientation functions (MD-TD).
It is clearly seen that in all the three sLLDPE resin films the MD tear strength does not correlate with the crystalline
orientation in the films. At high draw-down ratio the crystalline orientation is seen to increase in MD and the MD
tear strength also increases. On the contrary all other LLDPE films show a decrease in MD tear strength at higher
draw-down.
900
sLLDPE1
800
sLLDPE2
MD Tear (gm/mil)
700
sLLDPE3
600
Z‐N LLDPE1
500
Z‐N LLDPE2
400
mLLDPE
300
Sup Hex LLDPE
200
100
0
0
0.05
0.1
0.15
0.2
faMD‐faTD
Figure 4: Relation between MD tear strength and the crystalline orientation
Small data point: low DDR (10.4); Large data point: high DDR (30.5)
We observed that the MD tear strength of LLDPE blown films did not show correlation with any of the crystalline
axes or with the amorphous phase chain orientation alone. But, as seen in Figure 5 and Table 3, it shows reasonably
good correlation with the MD/TD birefringence. The birefringence values indicate the sum of the contributions from
both these phases. In the case of sLLDPE films, the overall orientation of polymer chains seems to increase in TD at
higher draw-down, which results in higher MD tear strength. In Z-N LLDPE films the overall orientation at higher
draw-down (as indicated by birefringence) increases towards MD, which gives poor MD tear characteristics to the
films. In super hexene-LLDPE films the birefringence at low draw-down is already significantly in TD. This gives
high MD tear properties to these films even at low draw-down ratio. Increasing polymer chain orientation further in
TD may not be effective in further enhancing the MD tear strength of super hexene-LLDPE films.
900
sLLDPE1
800
sLLDPE2
MD Tear (gm/mil)
700
sLLDPE3
600
Z‐N LLDPE1
500
Z‐N LLDPE2
400
mLLDPE
300
Sup Hex LLDPE
200
100
0
‐15
‐10
TD
‐5
0
5
10
‐4
Birefringence (X10 )
15
20
MD
Figure 5: Relation between MD tear strength and film birefringence (MD-TD)
Small data point: low DDR (10.4); Large data point: high DDR (30.5)
Transverse Direction Tear Strength:
The TD tear strength of the LLDPE films correlated well with the crystalline orientation function of a-axis of unit
crystal. As shown in Figure 6, higher draw-down ratio in all the films results in higher MD crystalline orientation,
which results in higher TD tear strength.
1200
TD Tear (gm/mil)
1000
sLLDPE1
800
sLLDPE2
600
sLLDPE3
Z‐N LLDPE1
400
Z‐N LLDPE2
200
mLLDPE
Sup Hex LLDPE
0
0
0.05
0.1
0.15
0.2
faMD‐faTD
Figure 6: Relation between TD tear strength and the crystalline orientation
Small data point: low DDR (10.4); Large data point: high DDR (30.5)
CONCLUSIONS
In LLDPE resin films, we observed that MD tear strength correlates with the overall orientation of the polymer
chains in the film plane, which includes the orientations in the amorphous phase and the crystalline phase. The
overall MD/TD orientation can be evaluated by analyzing the films for birefringence using optical microscopy. The
TD tear strength of the films depends strongly on the crystalline phase orientation as indicated by the a-axis
orientation of the unit crystal of polyethylene.
We observed that when sLLDPE films are blown at higher draw-down conditions, they show an increase in
crystalline MD orientation as well as an increase in overall polymer chain orientation in TD. This phenomena results
in higher TD tear strength as well as higher MD tear strength. Z-N LLDPE resin films when blown at higher drawdown show higher crystalline and overall orientation in MD, which results in higher TD tear strength in these films
but the MD tear strength is reduced. The anomalous and counter intuitive enhancement in tear properties of sLLDPE
films may be attributed to their unique resin architecture and morphology.
References
1. Chen H. Y., Bishop M. T., Lands B. G., Chum S. P., “Orientation and Property Correlation for LLDPE Blown
Films”, J. Appl. Polym. Sci., 101, pp 898-907(2006).
2. Krishnaswamy R. K., Sukhadia A. M., “Orientation Characteristics of LLDPE Blown Films and their
Implications on Elmendorf Tear Performance”, Polymer, 41, pp 9205-9217(2000).
3. Krishnaswamy R. K., Lamborn M. J., “Tensile Properties of Linear Low Density Polyethylene (LLDPE) Blown
Films”, Polym. Eng. Sci., 40(11), pp 2385-2396(2000).
4. Choi K-J., Spruiell J. E., White J. L., “Orientation and Morphology of High Density Polyethylene Films
Produced by Tubular Blowing Method and its Relationship to Process Conditions”, J. Appl. Polym. Sci., 20, pp
27-47(1982).
5. Kwack T. H., Han C. D., “Development of Crystalline Structure during Tubular Film Blowing of Low Density
Polyethylene”, J. Appl. Polym. Sci., 35, pp 363-389(1988).
6. Patel R. M., Butler T. I., Walton K. L., Knight G. W., Polym. Eng. Sci., 34(19), pp 1506-1514(1994).
7. Zang X. M., Elkoun S., Aji A., Huneault M. A., “Oriented Structure and Anisotropy Properties of Polymer
Blown Films: HDPE, LLDPE and LDPE”, Polymer, 45, pp 217-229(2004).
8. White J. L., Cakmak M., “Orientation, Crystallization, and Haze Development in Tubular Film Extrusion”,
Advances in Polymer Technology, 8(1), pp 27-61(1988).
9. Hermans P. H. and Platzek P., Kolloid Z., 88, 68(1939).
10. Bunn C. W., Trans. Faraday Soc., 35, p 482(1939).
11. White J. L. and Spruiell J. E., “Specification of Biaxial Orientation in Amorphous and Crystalline Polymers”,
Polym. Eng. Sci., 21, pp 859-868(1981).
12. Pazur R. J.,, and Prud'homme R. E., “X-ray Pole Figure and Small Angle Scattering Measurements on Tubular
Blown Low-Density Poly(ethylene) Films”, Macromolecules, 29(1), pp 119-128(1996).
Unusual Enhancement in
Tear Properties of
Single-Site LLDPE Blown Films at
High Draw-Down Ratio
Presented by:
Name Norman Aubee
Title Technical Service Specialist
Company: NOVA Chemicals
Objective
„
Study the relation between crystalline and
amorphous orientations and tear properties
of LLDPE blown films
Materials
Product
Reference
Name
Comonomer
Melt Index
(gm/10min)
Density
(g/cm3)
SURPASS FPs016-C
sLLDPE1
Octene
0.65
0.9160
SURPASS FPr018-D
sLLDPE2
Octene
0.86
0.9180
SURPASS FPs117-C
sLLDPE3
Octene
0.92
0.9170
SCLAIR FP020-C
Z-N LLDPE1
Octene
0.67
0.9210
SCLAIR FP120-C
Z-N LLDPE2
Octene
0.93
0.9200
COMP mLLDPE
mLLDPE
Hexene
1.18
0.918
NOVAPOL TD-9022-D
Sup hex
LLDPE
Hexene
0.64
0.9195
Experimental
„
„
„
Films produced on a Macro 8” blown film line with
dual lip air ring and IBC
General-purpose spiral die with die gap 50 mil
Elmendorf tear strength as per ASTM D1922
Film gauge
(mil)
Blow-Up
Ratio
Line Speed
(ft/min)
Draw-Down
Ratio
Low DDR Film
1.5
3:1
130
10.4
High DDR Film
0.75
2:1
390
30.5
Film Characterization
„
Overall crystalline and amorphous orientation:
Birefringence by retardation of light through the film
in MD and TD using polarized light microscopy–
ASTM D 4093 – 95
„
„
Crystalline Orientation: Orientations functions of
three crystalline axis by GADDS Pole Figure
analysis
Amorphous Orientation: Calculated from overall
orientation(birefringence), crystalline orientation(GADDS
Pole Figure) and film crystallinity (Raman Spectroscopy)
Polyethylene Crystal Structure
„
a, b and c -axes define
„
unit cell
Chain axis is aligned
with c -axis
Crystalline Orientation
„
General Area Detector Diffraction System
(GADDS) Pole Figure analysis
A
1
White-Spruiell representation of
crystalline axes orientations
D
TD →
0.5
E
G
B
0
-1
-0.5
0
0.5
-0.5
F
-1
C
MD →
1
A: TD only
B: MD only
C: ND only
D: MD/TD equi-biaxial
E: TD/ND equi-biaxial
F: MD/ND equi-biaxial
G: isotropic
GADDS Pole Figure – Example
„
White-Spruiell representation of crystalline axes
orientations for Z-N LLDPE1
a -axis : MD oriented
b -axis : in TD/ND plane
c -axis : Isotropic
Amorphous Phase Orientation
„
Subtract the two equations to get amorphous phase
orientation (fam,MD − famTD)
Δ MN = nM − nN = w[Δocbc f cc, MD + Δocab f ac, MD ] + (1 − w)Δoa f am , MD
Δ TN = nT − nN = w[Δ f
oc
bc
c
c ,TD
+Δ f
oc
ab
c
a ,TD
] + (1 − w)Δ f am ,TD
oa
w : film crystallinity (by Raman spectroscopy)
nM , nN , nT: refractive indices in Machine, Transverse and Normal direction of film
fcc, fac – crystalline orientation functions of c and a-axis of PE unit crystal
Δocbc , Δocab are intrinsic birefringence values of PE crystals in respective direction
Δocbc = 0.056, Δocab = −0.005
Δoa intrinsic birefringence of amorphous phase = 0.058
Δ MN − ΔTN = nM − nT = MD/TD Birefringence (by Optical Microscopy)
Results: Crystalline Orientation
„
Unit Crystal Orientation Functions
Small data point: Low DDR (10.4)
Large data point: High DDR (30.5)
MD Tear and Crystalline Orientation
„
„
MD Tear strengths of sLLDPEs do not correlate with
a-axis orientation
MD Tear strength of sLLDPE films increases with
increase in DDR
Small data point:
Low DDR (10.4)
Large data point:
High DDR (30.5)
MD Tear and Crystalline Orientation
„
MD Tear strength of all LLDPE films
correlates with MD/TD birefringence
Small data point:
Low DDR (10.4)
Large data point:
High DDR (30.5)
MD Tear Strength
„
„
MD Tear strength of sLLDPE increases at higher DDR
MD Tear strength of Z-N LLDPE decreases at higher DDR
TD Tear Strength
„
TD Tear strength of LLDPE films correlates
with crystalline a-axis orientation
Small data point:
Low DDR (10.4)
Large data point:
High DDR (30.5)
Conclusions
„
„
MD tear strength correlated with the overall
orientation of polymer chains in LLDPE films
as analyzed by birefringence
TD tear strength of LLDPE films correlated
with the a-axis orientation of unit crystal
Conclusions
„
„
„
At high DDR sLLDPE films showed higher a-axis
orientation in MD but higher overall polymer chain
orientation in TD
Above mentioned phenomena resulted in higher
MD and higher TD tear strength of sLLDPE films
at high DDR
Z-N LLDPE films showed increased a-axis
orientation and higher overall polymer chain
orientation in MD with increase in DDR, which
resulted in poor MD tear
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